Toro Rosso team principal Franz Tost says both Jaime Alguersuari and Sebastien Buemi are progressing, but that a decision on their futures won't be taken until the end of the season.

With another driver from the Red Bull stable - Daniel Ricciardo - being promoted to a race seat with HRT, Alguersuari and Buemi are under pressure to perform. Both managed to finish in the top ten in the last race at the Hungaroring, but Tost told the Official Formula One website that he would be evaluating their performances throughout the rest of the season before deciding who will drive for the team next year.

"They are moving forward," Tost said. "That was clearly visible in the last couple of races, with the last race seeing both of them in the points - so let's wait and see how the second half of the season works out. Then at the end of the year we will sit together with Red Bull to discuss who will sit in our cars in 2012."

With Toro Rosso acting as a breeding ground for young Red Bull-backed drivers, Tost said that there was a timeframe in mind for a driver to prove themselves.

"Maximum three years. Or let's put it this way: if you are not sure after three years whether he's going to make it, I would bluntly say forget him, period. Three years - why? Because this is the time a driver needs today in Formula One to develop from a rookie into a calculable factor in the team."

Despite praising both of his current drivers, Tost did admit to keeping a close eye on Ricciardo's progress, and expected to see an improvement in the next couple of grands prix.

"Well, I think Sebastien and Jaime are doing a good job and I am also really looking forward working together with the other Red Bull youngsters, Daniel Ricciardo and Jean-Eric Vergne. Both have done the young drivers' days with Toro Rosso last year in Abu Dhabi and Daniel was our third man before he got the opportunity to race for HRT. I expect him to best Liuzzi after not more than three or four races."